Hypersonic flight: Chinese scientists create prototype with an engine design abandoned by Nasa

The concept by Chinese-born engineer Ming Han Tang was largely neglected by the US government, but in China the design has attracted increasing attention
Purge of Chinese researchers in the US coincided with the start of China’s hypersonic weapons programme, say some Chinese space scientists

Science

Stephen Chenin Beijing

Published: 5:00am, 9 Dec 2021

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A research team in China has built and tested a prototype hypersonic flight engine based on a bold design by a Nasa scientist more than two decades ago.

Unlike most hypersonic aircraft with an engine at the belly, the Two Stage Vehicle (TSV) X-plane proposed by Ming Han Tang – then chief engineer of Nasa’s hypersonic programme in the late 1990s – was driven by two separate engines on the sides.

The engines could work as normal turbine jet engines at lower speed and then switch to a high-speed mode which has no moving parts as the aircraft accelerates to five times the speed of sound, or beyond.

The prototype based on Tang’s blueprint was tested at a wind tunnel in Nanjing, Jiangsu. Photo: Nanjing University of Aeronautics and Astronautics

The aerodynamics of the dual-engine design was sophisticated and some important questions – such as whether the engines could ignite after switching to the hypersonic speed – remained unclear. The Boeing Manta X-47C, a programme to verify Tang’s design, was terminated by the US government in the early 2000s over technical difficulties and cost.

Professor Tan Huijun and his colleagues, at the Nanjing University of Aeronautics and Astronautics in the eastern province of Jiangsu, have built a prototype machine with a pair of side-opening air inlets based on Tang’s blueprint that was declassified in 2011.

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Tan, who has received a top government award for his contribution to China’s hypersonic weapons programme, tested the prototype in a wind tunnel that could simulate flight conditions from Mach 4 to Mach 8 for several seconds. They found the engines could start under some of the most challenging flight conditions, just as Tang predicted.

Tang’s idea had been largely neglected by the US government, but in China the design attracted increasing attention because “understanding its work mechanism can provide important guidance to hypersonic plane and engine development”, Tan and colleagues said in a paper published in the Chinese peer-reviewed Journal of Propulsion Technology on Sunday.

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Tang was born in Chongqing, China’s wartime capital, to Zi Chang Tang, a Nationalist Army general. At the end of the Chinese civil war, his family moved to Taiwan and Brazil before eventually settling in the United States in the 1950s.

Tang started as an aerospace engineer at Nasa’s Dryden Flight Research Centre in California in the 1960s and worked his way up to leading positions at Lockheed Martin’s top secret programmes for the development of high-speed spy planes, including the U-2 and SR-71 Blackbird.

From the late 1980s, Tang headed hypersonic flight research programmes at Nasa while overseeing the agency’s collaboration with the US Air Force.

Tang left Nasa in 1999, a year when mistrust of ethnic Chinese scientists reached a new height in the US.

Wen Hoo Lee, a nuclear physicist with the Los Alamos National Laboratory in New Mexico, was indicted for providing US nuclear weapon secrets to China. Though he was later cleared of the charge and received an apology and a US$1.6 million settlement from the US federal government, the case was widely reported and affected many researchers with a Chinese background, especially those working in sensitive facilities.

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Chen Shiyi, then the deputy director of the Centre for Nonlinear Studies at Los Alamos and one of the world’s top experts on turbulence, quit the same year. Chen eventually returned to China and helped establish advanced hypersonic research laboratories.

The purge of Chinese researchers in the US coincided with the start of China’s hypersonic weapons programme in the early 2000s, according to some Chinese space scientists.

Tang worked as a consultant after leaving Nasa. He died in Williamsburg, Virginia, in 2018 aged 79.

Tang’s design was not perfect, according to Tan and his colleagues. Computer simulation and experimental results suggested strong turbulence could occur around some corners in the air inlet, affecting flight stability.

There was also a limit to how steeply a plane could climb without choking the engines. Though the dual-engine layout was feasible with some advantages, as the ground experiment suggested, many challenging issues still had to be resolved, Tan’s team said.

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China’s hypersonic weapons mostly use a rocket in the initial stage of flight. After reaching a high altitude at high speed, the rocket shuts down and lets the air-breathing engine take over.

But Yin Zeyong, director of science and technology at the Aero Engine Corporation of China in Beijing, said China was also rapidly building its capability to develop and test turbo jet engines that could fly at Mach 3-4 to work with or replace the rocket in a hypersonic flight.

Chinese space authorities plan to build a plane that can transport 10 passengers to anywhere on the planet in an hour by 2035.

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Although there were many challenges – such as reaching a high temperature and being complex in structure – hypersonic engines built around turbojet technology, known as turbine-based combined cycle, “can be a more feasible and optimal choice”, Yin said in a paper published in the Chinese peer-reviewed journal Aeroengine in August.

In July, the US Air Force awarded private start-up company Hermeus a US$60 million contract to develop a prototype aircraft with similar technology in three years. The Hermeus Quarterhorse aims to reach Mach 5 with one engine.